For convenience of portability, a laptop computer usually has a touchpad near a keyboard to replace a mouse as an input device. Users are not limited to the environment where they use the laptop computer and free from inconvenience that the mouse has to be carried all the way. However, touchpads have defects such as low sensitivity and easy affection by environment. Most users would like to use a mouse rather than a touchpad.
A touchpad generally comprises two portions: a touch detecting unit and a touch control unit. The touch detecting unit is used for detecting and receiving touch control location data from users. Then, the touch control location data is sent to the touch control unit. By the touch control unit, the location data is converted into a coordinate. The coordinate is sent to an operating system (OS) of a computer to control location of a cursor. A common touchpad utilizes resistance, capacitance, infrared ray, or surface acoustic wave.
However, characteristics of the touchpad are easily influenced by change of the atmospheric pressure to affect operation sensitivity. For example, when the atmospheric pressure becomes lower, human body will lower its internal pressure to adapt to the change of the atmospheric pressure. It causes change of conductivity in the human body. When a capacitive touchpad is used, due to reduction of coupled capacitance formed between the human body and the touchpad, sensitivity of the touchpad decreases accordingly. Hence, users need to exert larger force. On the other hand, when the atmospheric pressure becomes higher, users merely need to exert smaller force.
As to a resistive touchpad, the principle thereof is pressure detection on the surface of the touchpad. After voltage transformation, the touch location can be calculated. When the atmospheric pressure becomes lower, users need to exert larger force. When the atmospheric pressure becomes higher, users merely need to exert smaller force.
Therefore, under different atmospheric pressures, operating sensitivity of the touchpad will be affected. It is inconvenient for users to change their habit and force in using the touchpad.
Touchpads have lower sensitivity in moving. When the sensitivity is increased, precise positioning can not be achieved. Sensitivity and positioning precision will be affected by user contact area. Additionally, when a current touchpad is used to move the cursor, fingers are needed to draw back and forth on the touchpad to move the cursor. When the cursor needs to be moved a longer distance, it is inconvenient for the fingers to draw back and forth many times.
Since traditional touchpads are easily influenced by the change of the environmental atmospheric pressure or sweats from the fingers to affect operation sensitivity and positioning precision, it is necessary to provide a touch control device having sensitivity irrespective of change of the environmental atmospheric pressure. Meanwhile, it can provide better control over sensitivity so that a laptop computer can control the cursor with high sensitivity without the aid of a mouse.
Therefore, in order to solve problems mentioned above, US Patent Publication No. 2008/0068332 provides a new touchpad device to control the cursor on the screen. Please refer to FIG. 1. The invention uses a light source to scan a moving template and reflected light beams from the moving template to calculate movement and location of the cursor corresponding to displacement of the moving template. In addition, there is an automatic homing device for fixing the moving template in a certain point so that the template can be further used to control the cursor. However, the automatic homing device in this invention doesn't conform to usual practice. There is no detailed study on relation between cursor displacement speed and edge contacting time of the touchpad. It causes new problems and becomes more inconvenient.